Electrically small high-temperature superconducting Y-Ba-Cu-O meander dipole antennas for ...

232 Pages·2012·20.27 MB·English

by  Mazlina Esa

ELECTRICALLY SMALL
HIGH-TEMPERATURE SUPERCONDUCTING Y-Ba-Cu-O
MEANDER DIPOLE ANTENNAS
FOR SPACE-LIMITED APPLICATIONS
MAZLINA ESA
A thesis submitted to the Faculty of Engineering
of The University of Birmingham
for the degree of
DOCTOR OF PHILOSOPHY
School of Electronic and Electrical Engineering
University of Birmingham
Edgbaston
Birmingham
B152TT
England
August 1996
University of Birmingham Research Archive

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SYNOPSIS
Two sets of electrically small antennas in the form of coplanar meander dipoles have been
designed and tested in this study. The meander dipoles are the anti-symmetrical and the
symmetrical meander structures. Both sets were based on the 1.0 GHz linear half-
wavelength dipole, i.e., all the meander dipole antennas have equal total arm lengths of
150.0 mm. Each set consists of several antennas, with different number of meander sections.
The anti-symmetrical meander antennas were fabricated from copper (on RT/duroid
substrate) whilst the symmetrical meander antennas were fabricated from copper, thick- and
thin-film high temperature superconducting (HTS) materials. The first type of meander
antennas was fed from underneath the circuit, through the substrate. The meander antennas
are electrically small. However, as the physical size decreases, the frequency of operation
increases resulting in an electrical size increase. The antennas were found to be inefficient,
which is inherent to their small size. In addition, the far-field radiation pattern was close to
that of a short dipole. Although they are inefficient as compared with large antennas, they
can potentially have increased gain and increased efficiency with the use of superconducting
material. This potential has been demonstrated by the second design, even though they have
much smaller electrical and physical size. Coplanar strip (CPS) feeding line was employed to
help reduce radiation pattern distortion. No matching network was designed because the
antennas are reasonably well-matched to the input. Instead, a quarter-wavelength sleeve
balun was incorporated to reduce the feeding loss and stray radiation. It also behaves as a
matching network. The HTS symmetrical meander antennas were found to outperform the
corresponding copper structures in terms of gain and efficiency. They also exhibit the
supergain ratio in the range 10 to 45 over the corresponding copper structures. The
symmetrical meander antennas operate at almost the same frequency as that of a linear half-
wavelength dipole which has the same track length. This shows that the linear dipole can be
miniaturised by meandering its radiating structure, whilst maintaining the frequency of
operation. Numerical simulations were also done on all the designed antennas. The
suitability of the HTS meander antennas for space-limited applications has been
demonstrated.
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ACKNOWLEDGEMENTS
I would like to thank Dr M. J. Lancaster for giving such a wonderful guidance
throughout the work done in preparation of this dissertation. I would also like to extend my
gratitude to Dr L. P. Ivrissimtzis (now at COMSAT RSI, CSA Antenna Systems, Kent) for
being such a great help. I am also grateful to Dr F. Huang for his valuable assistance
especially during the second year of this study. Stimulating discussion sessions spent with
Dr J. S. Hong, Prof. P. S. Hall, Dr C. C. Constantinou and Dr D. G. Checketts are greatly
appreciated. Much thank to all members of the Superconductivity Group and the previous
COPS group; for their co-operation and worthy help.
In addition, I would like to thank the Universiti Teknologi Malaysia, Malaysia, and
the Malaysian Government for approving my study-leave and sponsoring my studies.
CONTENTS PAGE
CHAPTER 1 INTRODUCTION 1
1.0 OBJECTIVES AND SCOPE OF STUDY 1
1.1 SMALL ANTENNAS 4
1.2 SMALL MEANDER ANTENNAS 10
1.3 LOW-TEMPERATURE SMALL SUPERCONDUCTING ANTENNAS 14
CHAPTER 2 ANTENNA PROPERTIES 16
2.0 INTRODUCTION 16
2.1 RADIATION PATTERN 16
2.2 DIRECTIVITY AND GAIN 21
2.3 INPUT IMPEDANCE 22
2.4 MATCHING NETWORKS 25
2.5 EFFICIENCY 28
2.6 BANDWIDTH 29
2.7 SMALL ANTENNAS 30
2.8 DIPOLES 34
2.8.1 Short Dipoles 34
2.8.2 Half-wavelength Linear Dipoles 44
2.8.3 Meander Dipoles 49
2.8.4 Meander Dipoles with a Feed Line 54
CHAPTER 3 SUPERCONDUCTING ANTENNAS 57
3.0 INTRODUCTION 57
3.1 SUPERCONDUCTIVITY 57
3.2 SURFACE IMPEDANCE AND PENETRATION DEPTH 60
3.3 SURFACE IMPEDANCE OF SUPERCONDUCTING FILMS WITH
FINITE THICKNESS 67
3.4 SMALL HIGH-TEMPERATURE SUPERCONDUCTING ANTENNAS 70
3.5 MATCHING NETWORKS 89
PAGE
CHAPTER 4 ANTENNA MEASUREMENTS 90
4.0 INTRODUCTION 90
4.1 GAIN 90
4.1.1 Absolute Gain 90
4.1.2 Gain by Comparison 93
4.1.3 Superdirectivity and Supergain 95
4.2 EFFICIENCY 97
4.2.1 General 97
4.2.2 HTS Circuits 100
4.3 RADIATION PATTERN 102
CHAPTER 5 ANTENNA DESIGNS 104
5.0 INTRODUCTION 104
5.1 ANTENNA GEOMETRIES AND DESIGN PROCEDURES 104
5.1.1 Anti-Symmetrical Meander Dipoles 104
5.1.2 Symmetrical Meander Dipoles 110
5.2 MATCHING NETWORKS 121
5.3 BALUNS 122
CHAPTER 6 NUMERICAL SIMULATIONS 126
6.0 INTRODUCTION 126
6.1 DESCRIPTION 126
6.2 EXAMPLES OF RESULTS 130
CHAPTER 7 MATERIALS AND
FABRICATION TECHNIQUES 131
7.0 INTRODUCTION 131
7.1 COPPER CIRCUITS 132
7.1.1 RT/Duroid 132
7.1.2 Fabrication Process 132
PAGE
7.2 THICK-FILM HTS CIRCUITS 133
7.2.1 YBCO/YSZ 133
7.2.2 Fabrication Process 133
7.3 THIN-FILM HTS CIRCUITS 134
7.3.1 YBCO/MgO 134
7.3.2 Pulsed Laser Ablation 13 5
7.3.3 Patterning and Etching Techniques 136
7.3.4 Silver Evaporation and Annealing Processes 137
7.4 CABLES AND CONNECTORS 138
CHAPTER 8 RESULTS AND DISCUSSION 139
8.0 INTRODUCTION 139
8.1 EXPERIMENTAL SET-UP 139
8.2 MEANDER DIPOLE ANTENNAS 145
8.2.1 Anti-Symmetrical Structures 145
8.2.2 Symmetrical Structures 161
8.2.3 Summary of The Comparison Between The Meander Dipole Structure 199
CHAPTER 9 CONCLUSION AND FUTURE WORK 201
9.0 INTRODUCTION 201
9.1 CONCLUSION 201
9.2 FUTURE WORK 203
APPENDICES 206
Appendix 1 Design Equations for Coplanar Strips 207
Appendix 2 Formulation of the Thick-Film YBCO Surface Resistance 209
Appendix 3 Miniature Superconducting Coplanar Strip Antennas for
Microwave and mm-wave Applications, presented at ICAP 95 210
Appendix 4 Electrically Small High-Temperature Superconducting
Meander Dipole Antenna, presented at EuCAS'95 213
PAGE
Appendix 5 Miniature Superconducting Printed Antennas for Space-Limited
Applications, submitted to Electronics Letters, July 1996 217
Appendix 6 Control Files for Pattern Generation on SONNET 219
Appendix 7 RT/Duroid Datasheet 221
Appendix 8 Properties of Dielectric Substrates Used for Growth of HTS Films 223
Appendix 9 Procedure for Patterning YBCO Thin-film on MgO 224
Appendix 10 Procedure for Applying Silver Contacts on HTS Thin-film
Devices in the Evaporator 226
Appendix 11 Microwave H20F Silver Epoxy Datasheet 227
Appendix 12 Program Listing of Far-field Radiation Pattern Measurements
using HP Basic 228
REFERENCES 230
CHAPTER 1 INTRODUCTION
1.0 OBJECTIVES AND SCOPE OF STUDY
The purpose of this study is to develop a practical printed electrically small antenna
made of high-temperature superconducting (HTS) material. HTS materials have low loss
characteristics superior to conventional conductors such as silver and copper. The use of
superconductors in the antenna construction does not predominantly affect their radiation
characteristics in terms of radiation pattern and directivity. This implies that the antenna
radiation resistance and external reactance are independent of the conducting material. The
material will, however, affect the input impedance, radiation efficiency and bandwidth of
particular types of antennas.
The advantageous characteristics of HTS antennas include small size, directive
radiation pattern in a small antenna, integrated low-loss matching, improved efficiency and
improved gain. It is useful to develop a planar antenna structure which can be flatly
mounted onto any body surface. For example, an antenna may have to be placed on the side
of an aircraft, where no protrusions are allowed. This antenna will then have a broadside
radiation pattern. Antenna miniaturisation has future potential since demands for small
antennas have been increasing in order to fulfil various specifications such as limited space
and portable equipment.
The objective of this study is to develop an electrically small HTS antenna with the
following characteristics and features:
high gain and high efficiency
dual-broadside E-plane radiation pattern
operational frequency in the region 1 to 10 GHz
integrated low-loss matching and balun
planar structure